1. Technical Field of the Invention
The present invention relates to a method and a system for estimating an attitude of a camera.
2. Related Art
In recent years, mobile devices having a large amount of processing for computing power, such as smartphones, have become rapidly popular. Most of these information terminals include a camera as an imaging device. The information terminals provide communication features that simply use audio information and text information. In addition, the information terminals also include communication features that use image information. In accompaniment with the growing popularity of such mobile devices, users are becoming increasingly familiar with technology referred to as augmented reality (AR) and technology for restoring a three-dimensional shape of a subject from captured images. In AR technology, for example, when an image of a target object is captured by the camera in the information terminal, a comment related to the target object is superimposed on the image and displayed. For example, the following non-patent reference 1 reports a method for three-dimensional measurement using a red, green, blue, and depth (RGB-D) camera.
In technologies such as those described above, calibration of a coordinate system of an environment captured in a two-dimensional image and a coordinate system of an actual environment is performed. To perform the calibration, the position and the attitude of the user (camera) is required to be known.
Therefore, in the field of AR technology, a following method is proposed. In the method, a marker of which the position, shape, and color are already known is disposed in advance in the actual environment. An image of the marker is captured by the camera. The attitude of the camera is then estimated by the image being analyzed. Since the past, a rectangular marker has often been used as such a marker (for example, refer to the following non-patent reference 2).    [Non-patent reference 1] Lieberknecht S., Huber A., Ilic S., Benhimane S., “RGB-D Camera-based Parallel Tracking and Meshing,” The 10th IEEE and ACM International Symposium on Mixed and Augmented Reality, October 26-29 (2011)    [Non-patent reference 2] Kato, et al., “An Augmented Reality System and its Calibration based on Marker Tracking,” Journal of the Virtual Reality Society of Japan, Vol. 4, No. 4, pp. 607-616 (1999))
To calculate the attitude of the RGB-D camera using the marker, first, the rectangular area of the marker is recognized by the RGB-D camera. Then, the camera attitude is estimated using the coordinates of the apexes of the rectangle.
However, three-dimensional space has a front/back relationship in addition to the two-dimensional relationships that are up/down and left/right. Therefore, a state occurs in which an object that is present in front hides a subject that is behind it. This state is referred to as occlusion. In an environment having numerous cables and components, these cables and components cause occlusion to occur at numerous perspectives. When a portion of the marker is hidden as a result of occlusion, detection of the rectangular area becomes difficult. Accurate estimation of the camera attitude becomes difficult.